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单选题
Three coins are tossed at the same time. What is the probability that exactly two heads are face up?
A
1/8
B
1/4
C
3/8
D
1/2
E
5/8
参考答案
参考解析
解析：
First, list all the possible outcomes when three coins are tossed in the air. When a coin is tossed, there are two outcomes, Heads or Tails. When three coins are tossed, there are 2×2×2= 8 possible outcomes:
{HHH, HHT, HTH, THH, HTI', THT, TTH, TIT} Three of these outcomes have exactly two heads. Therefore, P (exactly two heads) =3/8.
First, list all the possible outcomes when three coins are tossed in the air. When a coin is tossed, there are two outcomes, Heads or Tails. When three coins are tossed, there are 2×2×2= 8 possible outcomes:
{HHH, HHT, HTH, THH, HTI', THT, TTH, TIT} Three of these outcomes have exactly two heads. Therefore, P (exactly two heads) =3/8.
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